The purpose of this research is to develop the application of ambulatory blood pressure measurement in the management of essential hypertension. Conventional office blood pressure measurements are influenced by transient states of psychophysiological arousal evoked in the course of medical examination which may contribute to the difficulty in making prognosis on the basis of office blood pressure readings. Our laboratory developed a portable, patient-operated, semi-automatic blood pressure recorder which provides a representative sample of ambulatory blood pressure measurements throughout the day. The present research explores the prognostic value of initial ambulatory pressures in both treated and untreated hypertensive patients, while controlling for differences in office pressure, age, sex, and other factors presumably related to the risk of developing cardiovascular-renal complications. Analyzing clinical follow-up data for patients whom we saw in years prior to the advent of effective oral antihypertensive drugs, we also intend to document the rate of development of complications over a wider range of pressures than can presently be observed in untreated patients, and we plan to compare the incidence rates in this sample with those of our treated prospective sample in order to gauge the effectiveness of antihypertensive drugs in preventing cardiovascular-renal complications.